What did the cabinet decide overnight?

The prime minister said it was the most appropriate course as Mr Fenech had made allegations against the PM's former chief of staff, Keith Schembri – who resigned last week and was arrested on Tuesday.

"I left the final decision with my colleagues, who decided that it's not fitting to grant a pardon," Mr Muscat announced at a press conference, flanked by ministers.

He stressed that his cabinet had followed the advice of the chief of police and the attorney general.

Police confirmed on Thursday that Mr Schembri had been released and was no longer of interest to investigators.

The prime minister also reiterated his promise to resign only when those who had ordered the killing had been identified.

"I have made a very firm commitment that I want this case to be closed under my watch. I think the authorities have already delivered what many thought could not be delivered, that is a major breakthrough in the investigation. My job is to see this investigation concluded," he said.

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Angry protesters gathered outside the government palace in the early hours of Friday morning. One of Caruana Galizia's sons threw fruit at the car of a government minister and shouted insults, Reuters news agency reports.

Mr Fenech has filed a request for President George Vella, and not the cabinet, to consider his request for a pardon, alleging a conflict of interest. A court is due to consider his request on Friday afternoon.

Why have events come to a head?

Investigations into Caruana Galizia's murder intensified when a suspected middleman was pardoned on Monday.

The prime minister told parliament the suspect, Melvin Theuma, was being given immunity in return for information about the killing. Maltese reports suggested he had audio recordings linked to the case.

On Tuesday, Tourism Minister Konrad Mizzi resigned and Economy Minister Chris Cardona took the decision to suspend himself after being questioned by police on Saturday. They deny involvement.

Mr Muscat's chief aide, Keith Schembri, who had previously been named in the Panama Papers, quit.